rmp_frontend attribute check

Hello,

Thank you for your plugin!

Could you check if the rmp_frontend variable exists at the beginning of your javascript file ?

jQuery( document ).ready( function( $ ) {
  if (typeof rmp_frontend === 'undefined') {
    return;
  }
  //...
}

It would be useful when we want to merge all our javascript files and load the merged file in every pages, even when we don’t use rmp.

Thank you!